The present invention relates to a scroll compressor, and, more particularly, the invention relates to an Oldhams ring having a configuration which allows it to be manufactured more easily and with a reduced cost, thereby improving the productivity and cost of manufacture of a scroll compressor in which it is installed.
A scroll compressor has an Oldhams coupling which operates as a rotation-prevention mechanism for holding the rotation scroll. A typical scroll compressor of the type to which the present invention is directed will be described with reference to FIG. 6, which shows a cross section of the compression mechanism unit of the scroll compressor.
In a scroll compressor, as shown in FIG. 6, a crank shaft 15 is inserted in a bearing part 13a of a frame 13, and an eccentric member 15a of the crank shaft 15 is inserted in the bearing part 12b of a rotation scroll 12. The keys 14a of the Oldhams ring 14 that forms the Oldhams coupling are inserted in keyways 13b provided in frame 13 and keyways 12c provided in frame 12c, and the fixed scroll 11 is secured by a bolt 16 to the frame 13 in a state in which it engages with the rotation scroll 12.
A wrap 11a of vortex shape forming part of the fixed scroll 11 and a wrap 12a of vortex shape forming part of the rotation scroll move relative to each other due to the rotating motion, so that a gas is sucked in through a suction mouth pipe 18 provided in the fixed scroll 11, and the gas is compressed as it advances toward the center of the unit. The gas that is compressed is discharged from a discharge opening 11b at the center of the fixed scroll.
The scroll compressor shown in FIG. 6 operates as a compressor. The Oldhams ring 14 is formed to have the Oldhams coupling structure in that keys 14a are installed at both sides of the ring 14 and are inserted in the keyways 13b, 12c of the frame 13 and the rotation scroll 12. Therefore, with this Oldhams coupling structure, the rotation scroll 12 does not rotate, and the rotating motion of the rotation scroll 12 can be performed for the fixed scroll 11. An example of an Oldhams ring for a scroll compressor having the above structure is shown in JP-A-1-30518, wherein the Oldhams ring is manufactured by sintered metal molding, and cutting work or grinding is performed later on surfaces of the ring.
The sintered metal molding process molds a metal powder using a metal mold, and the molded metal is heated later to sinter the metal powder. A molding of sintered metal can accommodate a complexity and achieve a high precision in the molding of goods in the technical range that is achieved when a metal is molded by a die. But, the precision achieved in the molding of a sintered metal is inferior to the high precision that is attained by cutting work or grinding work. An efficient scroll compressor needs to be made of parts of high precision. Thus, it is necessary to do cutting work or grinding work to make the dimensions of the Oldhams ring and the precision of the shape precise when the Oldhams ring is formed by molding a sintered metal.
The problems associated with such manufacture will be explained by reference to the perspective view of the Oldhams ring shown by way of example in FIG. 7. An end face 14c of the Oldhams ring 14 shown in FIG. 7 is a which comes into contact face with the frame (not shown), and there is also a ridge line 14d with a key side face 14b on the same plane. The key 14a engages with the keyway of a frame (not shown) by way of the key side face. Therefore, the key side face 14b needs to be made even with the ridge line 14d in the neighborhood of the end face 14c. That is, the ridge line 14d needs to be processed to form a precise sharp corner. Thus, by cutting work or grinding work, both the key side face 14b and the end face 14c are processed, and the ridge line 14 is formed as a sharp corner.
In the process in which the Oldhams ring is manufactured of a sintered metal, the metal powder is molded by using a metal die to obtain the required shape. But, part of the ridge line 14d of the Oldhams ring is influenced by chamfering or a roundness provided in the metal die to improve the strength of the die. Thus, it is necessary to process both of the key side face 14b and the end face 14c to remove material from this ridge line 14d. Therefore, the conventional Oldhams ring is typically obtained by cutting or grinding both the key side face 14b and the end face 14c.
Then, if a ferrous metal is used, such as iron, a method of steam treatment may be employed as one of the surface treatment methods to be applied to the sintered ring. Steam treatment is a method of acidifying iron in high-temperature steam and forming a skin film of Fe304 thereon. According to this processing, the Oldhams ring can exhibit an improved wear resistance on slide surfaces due to the presence of an oxide film, and the function of preservation of the ring can be attained. While the volume of the Oldhams ring increases generally when a skin film of Fe304 is formed thereon by steam treatment, the volume increase is more evident at a sharp corner or edge than at other parts, with a result that the corner or edge swells after the steam treatment.
It was considered necessary, because the dimension is wrong when the buildup of the corner part occurs in the slide unit, for the slide unit to be processed after the steam treatment. Because the key side face 14b of each key 14a must engage in a keyway (not shown) so as to slide-freely, the key face 14b was processed and finished after the steam treatment. Here, the sintered metal is made from a metal powder, and it is not made to melt perfectly in the manufacturing process, so that holes are left in the metal powder. The holes in a sintered metal body range from the surface to the inside, and the skin film of Fe304 is formed on the inside as well as on the surface due to the steam treatment. Therefore, even if the surface is processed and partly removed after the steam treatment, there is a skin film of the internal portion Fe304 remaining on the surface, and so the wear resistance can be improved.
Therefore, it is typical that, in the case of performing a steam treatment on an Oldhams ring made of a sintered metal, the Oldhams ring is first sintered, and then the steam treatment is done and the cutting work or the grinding work is done later. A scroll compressor using an Oldhams ring on which cutting work or grinding work has been performed on both the key end face and the key side face, has the following problems.
The first problem is as follows. The sintered metal has holes, and the heat conductivity is wrong. Thus, the temperature of the tool becomes high during processing. And, a vibration easily occurs due to the intermittent processing caused by the presence of the holes. Thus, the ease of cutting is poor as compared with a powder material and melt goods formed of a steel product for the same component, etc. Therefore, the use of a sintered metal has the advantage that it is possible to achieve a very accurate shape for a final product obtained by molding with a die that is excellent in productivity. But it has a fault in that the wear on the tool is remarkable during processing. In this regard, a problem which occurs at the time of the cutting work on the Oldhams ring made of sintered metal using an end mill as a processing tool will be explained.
The part of an end mill where the wear is most remarkable is at the corner part of the cutting blade tip of acutent shape. On the other hand, as for the shape of a conventional Oldhams ring made of sintered metal, the ridge line between the key side face and the end face has pads, and so the machining allowance enlarges. This ridge line is processed by the corner part of cutting blade tip of the end mill. Therefore, the wear on the end mill is remarkable for processing a large part of the machining allowance of the hard sintered metal with the part of the end mill which is easiest to wear. And, as for the conventional Oldhams ring shape, the processing of the key side face and the end face is necessary.
When the end face processing using the lower edge of the end mill and the side face processing using an outer peripheral edge of the end mill are generally compared, the length where the corner of the cutting blade tip touches a part of the end face being processed is very long. Therefore, comparing the side face processing with the end face processing, the end mill wears more easily in the end face processing. That is, when the key side face and the end face are processed, during the end face processing the tool becomes remarkably worn compared to the tool wear which occurs during the key side face processing.
As described, because, in the processing, a large part of the machining allowance of the hard sintered metal is processed with the part of the end mill which is easiest to wear, that is, the processing occurs at the end face with the part of the tool which is easy to wear, the tool used to process the Oldhams ring of the conventional sintered alloy is remarkably worn and the productivity in the manufacture of the Oldhams ring is a problem.
When the Oldhams ring is processed with a grinder, that, when is the end face of the Oldhams ring is processed by using the end face of a cylindrical grinder, there is also a problem of very large wear at the corner part of the grinder. As for a scroll compressor using an Oldhams ring having this problem, there is a problem concerning the improvement of the productivity and the reduction of the cost.
The second problem is as follows. In the steam treatment to improve the wear resistance of a slide part, the volume increase produced by generation of the Fe304 causes a sharp corner to swell in size. When the steam treatment is done on an Oldhams ring which has sharp corners and edges in the slide portion, a processing to remove the buildup must be carried out after the steam treatment is done. But when the steam treatment is performed on a sintered metal, and Fe304 is formed, the tool wear becomes more remarkable and the processing becomes more difficult than for a sintered metal on which the steam treatment is not done. Therefore, the productivity of the Oldhams ring becomes much worse. This problem results in a further reduction in the productivity of a scroll compressor and a further increase in cost, added to the effects of the first problem.
The third problem is as follows. There is a problem of poor productivity of the scroll compressor and an increase in the cost of the compressor and an air conditioner which uses the scroll compressor as a result of the first problem and the second problem mentioned above.